Johannesburg - The first satellite transmission from a Bull shark captured and tagged in the Breede River estuary has been made near the island of Bazaruto, off the coast of Mozambique, the SA Shark Conservancy (SASC) said on Thursday.

The large, male Bull shark, which was tagged in March, had journeyed over 2000km (about 36km a day) to reach Mozambique, SASC and the Save Our Seas Foundation said in a joint statement.

“We have now shown this species migrates across international borders, whereby it becomes vulnerable to a multitude of fisheries and environmental pressures,” said SASC marine scientist Meaghen McCord.

“This is the first time the ecology and behaviour of Bull sharks has been studied in South Africa and we hope it assists with the development and implementation of management measures for this near-threatened species,” she said.

Up until now, it had only been speculated about where the Breede River population of Bull sharks migrated, if at all, said McCord.

There were few studies on African populations of these sharks, other than recordings made by the Natal Sharks Board via its beach netting program along the coast of KwaZulu-Natal.

The Bull shark, known locally as the Zambezi shark, was well-known worldwide for swimming far up rivers and thriving in low-saline water.

There had been sightings of Bull sharks in the Breede River over the years, however some locals disputed their existence and documented evidence had been scarce, McCord said.

The shark was tagged with a pop-up archival transponding (PAT) tag, inserted in the dorsal fin.

The tag released from the shark after a period of time, floated to the water's surface and transmitted data via satellite.

McCord said the tagging of the shark was made possible by a research grant from the Save Our Seas Foundation.

“(It) was very important to establish if the Breede River population was endemic to the area or indeed part of the larger population and, therefore, global gene pool.

“We are slowly beginning to gain insight into how this apex predator utilises river systems,” she said.

Estuaries played a critical role in the life-history of the Bull shark and protecting them would play a vital role towards maintaining ecosystem integrity in African waters, McCord said. - Sapa